The present invention relates to a piston assembly for an internal combustion engine. More particularly, the present invention relates to a piston assembly in cooperation with an oil piston cooling jet for effecting lubrication of the piston pin bushings.
A piston assembly for an internal combustion engine generally becomes very hot during use, and is subjected to relatively severe thermal stresses as compared to other engine parts, especially on its top wall or crown portion which is directly exposed to the heat of the gases in the combustion chamber that is partly defined by the piston. This problem of heating of the crown of the piston assembly has become more and more severe with modern internal combustion engines, due to increases in thermal loading arising from increases in engine power output. Various schemes have been developed in the past for aiding with the cooling of such a piston assembly and presently, some form of active cooling of the piston assembly is seen to be quite necessary.
In particular, the concept of cooling the piston crown from below by injecting a flow of engine lubricant up into the space defined by the cup-shaped piston structure, including the piston crown and the piston skirt, so as to impinge against the lower side of the piston crown and to cool it, has been put forward in the past in various forms. In particular, it has been recognized that it is helpful for such lubricant cooling of the piston crown to provide a shaker chamber near the lower surface of the piston crown which defines a reservoir for temporarily and intermittently accumulating a pool of lubricant therein. The lubricant from this pool is splashed by means of inertia against the piston crown as the piston reciprocates in the cylinder bore.
Lubrication of components other than the crown is also essential. Typically, a piston is connected at one end to a connecting rod. The connecting rod includes an eye having a small end bushing that receives a piston pin such that the connecting rod pivots through a relatively small pivoting angle of the piston pin during reciprocation. The other end of the connecting rod is pivotally coupled to the crank shaft which also pivots through a relatively small angle. One area where it is desired to provide lubrication and cooling in the internal combustion engine is between the piston pin of the piston and the bushings supporting the piston pin. Such bushings reside in both the connecting rod and the pin bores of the piston top.
It is known to indirectly supply a lubricant such as oil to the piston pin by splashing the oil proximate the piston pin area. In one form, oil that is sprayed onto the piston undercrown area specifically for cooling the piston crown splashes onto the connecting rod eye of the connecting rod. Since the connecting rod is exposed about the piston pin, the oil wicks into the connecting rod eye bushing area defined between the piston pin in the connecting rod eye to provide lubrication. While the splash method does supply lubricant to the piston pin area, the amount of lubricant supplied to the piston pin by the splash method may not be satisfactory. In order to alleviate what has been seen as insufficient cooling/lubrication by means of the splash method, some engines now employ an active or positive method providing lubrication to the piston pin. Such a method has its own trade-offs in that it usually involves defining passages that supply lubrication under pressure to the piston pin. Such passages can be complicated to define and connect with a source of lubrication under pressure. Such passages may also affect the strength of the piston pin.
In view of the foregoing, there is a need to provide adequate cooling and lubrication to the piston pin and the bushings that support the piston pin. The method of providing such cooling and lubrication should be as simple as possible, involving a minimal number of changes to an existing design. Defining new passageways for lubricating fluid under pressure in an existing engine block design can be exceedingly expensive.
The piston pin bushing cooler of the present invention substantially meets the aforementioned needs of the industry. It is a simple design that provides for intermittent, but adequate spray of lubricant on the piston pin area for both cooling and lubrication of the piston pin bushings in the piston pin bore as well as in the connecting rod. The cooler utilizes an existing oil jet provided for in the block of the engine in cooperation with a deflector defined in the piston skirt. The particular oil jet used generates a stream of lubricant that is angularly displaced from the longitudinal axis of the cylinder within which the piston reciprocates. As a result of being angularly displaced from the longitudinal axis, the footprint of the lubricant striking the underside of the piston crown traces a somewhat elongate pattern once each reciprocation of the piston. The deflector of the present invention is designed to intersect the stream of oil for only a portion of the reciprocation of the piston. For the remainder of the period of reciprocation of the piston, the oil stream is directed to the oil gallery adjacent the underside of the crown of the piston. When the deflector intersects the oil stream, the oil is deflected onto the piston pin area for cooling and lubrication of the piston pin bushings.
The present invention is a piston pin cooler for cooling and lubricating piston pin bore bushings that includes an oil jet, the oil jet directing a spray of lubricating oil toward the underside of a crown of a reciprocating piston for cooling the crown; and a deflector formed interior to a piston skirt presenting a deflector surface, the deflector surface intersecting the spray of lubricating oil for at least a portion of the duration of each reciprocation of the reciprocating piston and deflecting the intersected spray of lubricating oil to cool and lubricate the piston pin bushings. A notch extending toward the skirt is disposed adjacent the deflector to provide an opening for the cooling jet spray to pass through to the oil gallery during other portions of the piston movement. The present invention is further a deflector assembly, a piston skirt, and a method of cooling and lubricating piston pin bushings, especially the piston pin bore bushings.